The invention relates to a process for continuous treatment of objects in a processing unit, in particular for surface treatment of wafer-like objects such as semiconductor elements, preferably silicon wafers where the objects are moved along a conveyor track passing through the processing unit by a first linear-action conveyor device performing a back-and-forward movement and where the objects are supplied to/removed from the conveyor track by a transfer device. The invention further relates to an arrangement for continuous treatment such as surface treatment of objects arranged on supports, in particular wafer-like objects such as semiconductor elements, preferably silicon wafers, comprising a conveyor track passing through a processing unit and transfer devices for supplying/removing the supports to/from the conveyor track.
The surface treatment of objects is indispensable for the manufacture of a wide range of products in many fields of industry. The coating of objects with thin surface layers is particularly widespread, for preserving desirable product characteristics or ensuring them in the long term. Examples here are the coating of steel tools with thin abrasion-proof layers for reducing wear, or the coating of spectacle lenses with thin and optically active layers for reducing reflection. In the photovoltaics industry, solar cells are provided with thin surface coatings having a thickness of, for example, 80 nm, as a result of which their energy efficiency can be increased by up to 30% thanks to a number of physical effects.
Coating processes take place in some cases at atmospheric pressure, but frequently at low pressure. Low pressure is for example necessary to achieve sufficient homogeneity of the coating over the surface of the object. Also, it is frequently the case that certain deposition techniques are only possible at low pressure. A known coating process is low-pressure chemical vapor deposition. Here the surface coating grows from a reaction of one or more gases that are activated thermally or electrically in the form of plasma excitation.
The continuous coating on moving objects is used for improving the surface homogeneity of the coating. It is sufficient here for the coating device to be deposited homogeneously in one dimension, in particular in the direction transverse to the transport direction of the objects, By contrast, a two-dimensionally homogeneous deposition is required for coating on stationary objects, i.e. over the entire surface of the object. This leads to high extra expenditure from the technological viewpoint.
The steady movement of the objects relative to the coating source, necessary for a continuous coating, is achieved by a transport mechanism. The latter moves either the objects to be coated directly, or workpiece supports that receive those objects.
Workpiece supports for receiving the objects to be coated are used if the objects are not two-dimensional and/or the objects are fragile and/or the objects are not permitted to come into contact with the materials of the transport mechanism and/or the workpiece supports must perform a sealing function between the atmosphere and the low-pressure area. The workpiece supports used are as a rule plates made of steel, glass, graphite or ceramics and having recesses for receiving the objects.
Roller, chain and pusher drives can be used as the transport mechanism. In the case of the roller drive the preferably wafer-like objects or the workpiece supports run on a system of rollers that are actively driven.
In a chain drive, the objects are moved on a transport chain by drivers. Lightweight objects/workpiece supports can run directly on the chain. Above a certain weight, additional passively rotating rollers are used to take up the load.
In a pusher drive, the objects or workpiece supports are pushed through the treatment facility in a gap-free and endless line. Only the rearmost object/workpiece support is pushed in each case, and its movement is transmitted to all those in front of it. The pusher drive means that a continuous movement is not possible, since during the rearward movement of the pusher element the complete line of objects/workpiece supports stops. However, pusher drives are impervious to parasitic deposition and high temperatures.
With roller or chain drives, the transition from a timed to a continuous movement is achieved by operating the various roller to chain segments at differing speeds. This permits the use of these systems in low-pressure facilities which can insert and remove the objects/workpiece supports only in timed fashion via airlocks.
The roller or chain drive systems suitable for continuous transport present problems due to parasitic deposition and applications at high temperatures. Parasitic deposition occurs for example with plasma-supported low-pressure chemical vapor deposition. Only a disproportionately high expenditure can here prevent the roller bearings and/or chain links from also being coated and hence becoming hard to move in a very short time. If high temperatures are applied during processing of the objects, actively driven rollers or chains must be adequately protected from overheating. This too entails expensive measures.
The currently available workpiece supports present problems in facilities operating at high temperatures and high throughputs. To attain high resistance to warping at high temperatures, the workpiece supports must be of solid design. This gives them a high thermal capacity that leads to high energy losses when the supports are heated up and then have to be cooled down again outside the coating zone in quick succession. To achieve high throughputs in low-pressure facilities, the airlock chambers in which the supports are located must be evacuated as quickly as possible. This is critical if the airlock chambers have only one evacuation opening, for example due to technical reasons. In this case the air flowing out must flow around the support, thus slowing down the evacuation process. The provision of air flow apertures is only possible to a limited degree for stability reasons. In the case of wafer-like objects, the distance between the individual objects would also have to be increased. This is however undesirable for throughput rate reasons alone.
DE 43 03 462 C2 describes a multi-chamber coating facility in which substrates such as flat glass are treated. The substrates are here arranged spaced on supports and conveyed through the coating facility. To that end, slide elements such as rollers are provided that permit transportation at constant speed through the coating chambers.
U.S. Pat. No. 3,973,665 relates to a conveyor device for treatment of semiconductor substrates, for example by sputtering. To convey the objects, they are accommodated on supports that are conveyed at a distance from one another and in timed fashion. To that end, a conveying beam is provided for conveying the supports from one processing station to the next. It is furthermore necessary that the supports be gripped by further litters movable vertically to the movement of the lifting beam, so that the supports are disengaged from this beam when it moves back. Transport through airlocks is not possible.
GB 2 143 910 A relates to a system of supports that can be lined up to receive objects that are to be treated in a vacuum chamber. The supports themselves have geometrically adapted and interlocking edges that perform a sealing function during insertion into the vacuum chamber. Since the seals of the supports are not sufficiently high-temperature-proof, this system is unsuitable for high temperatures.
A conveying device is known from JP 10067429 A for substrates arrangable on a support that in turn is movable along rails by a spindle. A spindle drive for transporting wafers to be treated is also described in U.S. Pat. No. 4,947,784. The slides receiving the supports are passed through by the spindle. A transport device is known from DE 197 45 646 A1 that comprises shuttle conveyors and support lifting mechanisms for passing semiconductors through testing stations.
The problem underlying the present invention is to develop a process and an arrangement of the type mentioned at the outset such that continuous treatment like coating of two-dimensional objects in particular is possible with measures of simple design, with neither parasitic depositions nor high temperatures impairing the process sequence.
The problem is solved by the process substantially in that the objects are arranged on supports which are lined up on the conveyor track by at least two first linear-action conveying devices performing a back-and-forward movement and are then conveyed continuously through the processing unit, where the lining up and subsequent continuous conveying of the supports is performed such that one of the first conveying devices lines up a support transferred to the conveyor track with those supports already on the conveyor track while the other first conveying device continuously conveys the previously lined-up supports. The objects or supports themselves are conveyed through the processing unit at constant or almost constant speed.
In an embodiment of the invention, an object or a support carrying an object that exits the treatment or processing device is separated from the remaining lined-up objects by a second conveying device and aligned with a transfer device taking the objects or supports away from the conveyor track.
Pairs of pusher rods are preferably used as the first linear-action conveying device, and a pair of puller rods as the second conveying device.
An arrangement of the type mentioned at the outset is characterized in particular in that at least two first linear-action conveying devices performing a back-and-forward movement are assigned to the conveyor track for transporting the supports receiving the objects in front of the processing unit, and alternatingly line up individual supports in timed fashion with the supports lined up on the conveyor track and convey the lined-up supports continuously through the processing unit, and in that at least a second conveying device is assigned to the conveyor track for conveying of supports with treated objects, and separates the lined-up supports for alignment with the transfer device for removal of the support from the conveyor track.
Each support has a frame mounted on the guide rails determining the conveyor track.
In particular, the invention provides that consecutive supports on the conveyor track have differing receptacles for the first conveying devices, the latter being aligned with the supports in such a way that the support gripped by one of the first conveying devices remains ungripped by the other first conveying device and vice versa.
The first conveyor devices are here preferably designed as pusher elements such as plungers or rods preferably engaging by their front free ends in matched receptacles of the supports.
To that end it is provided in particular that viewed in the transport direction a first support of consecutive supports has a recess such as a groove running parallel to the transport direction that can be passed through by a first conveyor device, said recess or groove being aligned with a receptacle of the preceding support in the transport direction.
A further embodiment of the invention provides that the second conveyor device is designed in the form of puller elements such as plungers or rods. Here the second conveyor device can grip the supports using for example solenoids or mechanical couplings such as catches.
The first and/or second conveyor device can comprise a slide movable in particular by a spindle drive. The first and/or second conveyor device can also have an element such as a rod or plunger adjustable in a negative pressure range and connected via a vacuum seal with a drive such as a cylinder or spindle.
In accordance with a proposal that is inventive per se of the invention, the support receiving an object has a frame with corner pieces and frame elements such as ceramic rods connecting the latter, where diagonally opposite corner pieces are connected by tensioning elements.
The frame elements themselves are supported in sliding fashion on the rails forming the conveyor track.
Parallel tensioning elements such as wires tensioned by springs can extend from the frame itself as the support for at least one object. The clamping elements can here have fixing elements such as pressed-on metal balls for immobilizing the object.
The transfer device for placement/removal of the object onto/from the conveyor track can also be designed as a linear-action back-and-forward moving conveyor device in the form of, for example, a pusher rod or puller rod.
In detail, the arrangement comprises in particular three pairs of pusher rods, two pairs of puller rods and workpiece supports, where a transition from timed infeed of the workpiece supports to a continuous movement and in turn from the latter to a timed discharge is permitted by the pusher rods and puller rods. In this case, the workpiece supports can be pulled laterally onto a transport section by a pair of puller rods, and two parallel-operating pairs of pusher rods ensure a continuous movement of a gap-free row of at least two workpiece supports on the conveyor track, which in turn passes through by a processing unit that is traversed by the workpiece supports at a constant or almost constant speed. The workpiece supports themselves are, after passage through the processing unit, pulled by a pair of puller rods onto an end position of the conveyor track, from which position the workpiece supports are pushed off the conveyor track at the side by a pair of pusher rods.
The workpiece supports comprise a slide frame, with two differently shaped slide frames being transported alternatingly.
The conveyor track comprises a system of guide rails together with the slide frame form a sliding system.
Inside the slide frame of the workpiece supports, wires running parallel to one another are tensioned by springs and serve as supports for wafer-like objects. Metal balls can be pressed onto the wires themselves to define the position of the plate-like objects in the wire plane and to prevent any positional change of the objects themselves
With the teachings in accordance with the invention, a transport system of simple design is provided by means of which a gap-free row of workpiece supports can be conveyed through a processing unit at constant speed onto a conveyor track designed as a guide rail system. A corresponding transport system is uncritical in respect of high temperatures and parasitic deposition, since in the coating area itself that are no moving parts of the transport mechanism. By the interaction of two linear-action conveyor devices in the form of pusher rods performing a back-and-forward movement, in conjunction with two differently designed workpiece supports, a timed workpiece support movement, necessary for example for passage through a vacuum airlock system is transformed into a continuous movement at constant infeed speed for treatment of the objects.
Furthermore, workpiece supports are provided by the teachings in accordance with the invention that have a minimal thermal capacity and a maximum conduction value for a gas flow passing vertically through the support. The wires tensioned inside the slide frame have because of their low diameter a minimal mass, so that the energy loss due to heat discharge via the workpiece support mass is minimized. The tensioning of the wires using springs means that the wire section is completely warp-free even at high temperatures. Gas can flow besides the positioned objects and through the interstice between the wires. The conduction value for this gas flow is determined almost exclusively by the spacing of the positioned objects and is hence maximal for every predetermined spacing. This makes the workpiece support ideal for use in airlock chambers pumped on one side with high throughput requirements. A displacement of two-dimensional workpieces is prevented by simple means, e.g. by metal balls pressed onto the wires.